GTAW provides a shield gas that reduces effort in ionization of the welding arc, therefore it is common to see lower open circuit voltages used, High frequency arc starting is also a reason for GTAW to need lower open circuit voltage. SMAW requires arc initiation in an oxygen/nitrogen atmosphere and only gets its ionizing gas supply as the flux begins to be consumed.
Arc blow is almost always accentuated as current increases (more powerful flux fields) Also GTAW tends to be more common on thinner base metals that have less potential for becoming magnetized.
With DC TIG on steel, magnetic arc blow can be quite a problem when welding towards the end of a plate joint or in to a corner. However in general, lower current levels (and therefore less powerful magnetic forces), shorter arc lengths, and higher current densities tend to reduce magnetic arc blow issues when using DC TIG v Stick. With stick you have a relatively low current level coming off a relatively large diameter electrode with a relatively long arc length. Depending on these variables the arc can be "soft" and "fluffy" and easily pushed around by magnetic forces.
Whenever a current is passed through a conductor, a circular magnetic field is produced. The higher the current, the greater the intensity of the magnetic field and the greater the density of magnetic flux.
The strength of the magnetic field is approximated by magnetic permeability times the amperage. A ferromagnetic material, i.e. steel or iron can have a magnetic permeability between 1000 and 6000, with pure iron having a very high permeability.
Ohm's law indicates the higher the voltage for a given resistance, the higher the current.
Magnetic fields can be concentrated toward the end of a joint. Backing bars, end dams (prohibited by D1.1), etc. help to mitigate the concentration of the magnetic field near the end of a welded joint.
As noted in the other threads, GTAW tends to be used primarily on thin base metal, thus the welding currents tend to be lower and the magnetic fields have less intensity when compared welding processes used to joint thicker materials using higher welding currents. The intensity of the magnetic flux is also lower for nonferrous metals (low permeability) when the same welding current is used in comparison to welding a ferrous metal (high permeability). The lower the intensity, the less the influence of the magnetic field on the welding arc.
The problem can be compounded if more than one welding machine is connected to one end of the long member like a structural shape or pipe. The welding currents are additive.
Best regards - Al
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